Replace our hacked version of ax_pthread.m4 with latest upstream version.

Our version was different from the upstream version in that we tried to use
all possible pthread-related flags that the compiler accepts, rather than
just the first one that works. That change was made in commit
e48322a6, to work-around a bug affecting GCC
versions 3.2 and below (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8888),
although we didn't realize that it was a GCC bug at the time. We hardly care
about that old GCC versions anymore, so we no longer need that workaround.

This fixes the macro for compilers that print warnings with the chosen
flags. That's pretty annoying on its own right, but it also inconspicuously
disabled thread-safety, because we refused to use any pthread-related flags
if the compiler produced warnings. Max Filippov reported that problem when
linking with uClibc and OpenSSL. The warnings-check was added because the
workaround for the GCC bug caused warnings otherwise, so it's no longer
needed either. We can just use the upstream version as is.

If you really want to compile with GCC version 3.2 or older, you can still
work-around it manually by setting PTHREAD_CFLAGS="-pthread -lpthread"
manually on the configure command line.

Backpatch to 9.5. I don't want to unnecessarily rock the boat on stable
branches, but 9.5 seems like fair game.

aclocal.m4

 dnl aclocal.m4
 m4_include([config/ac_func_accept_argtypes.m4])
-m4_include([config/acx_pthread.m4])
+m4_include([config/ax_pthread.m4])
 m4_include([config/c-compiler.m4])
 m4_include([config/c-library.m4])
 m4_include([config/docbook.m4])

config/acx_pthread.m4

-dnl This is based on an old macro from the GNU Autoconf Macro Archive at:
-dnl http://www.gnu.org/software/ac-archive/htmldoc/acx_pthread.html
-dnl but it's been rather heavily hacked --- beware of blindly dropping in
-dnl upstream changes!
-dnl
-AC_DEFUN([ACX_PTHREAD], [
-AC_REQUIRE([AC_CANONICAL_HOST])
-AC_LANG_PUSH([C])
-acx_pthread_ok=no
-
-# We used to check for pthread.h first, but this fails if pthread.h
-# requires special compiler flags (e.g. on True64 or Sequent).
-# It gets checked for in the link test anyway.
-
-# First of all, check if the user has set any of the PTHREAD_LIBS,
-# etcetera environment variables, and if threads linking works using
-# them:
-if test x"$PTHREAD_LIBS$PTHREAD_CFLAGS" != x; then
-        save_CFLAGS="$CFLAGS"
-        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
-        save_LIBS="$LIBS"
-        LIBS="$PTHREAD_LIBS $LIBS"
-        AC_MSG_CHECKING([for pthread_join in LIBS=$PTHREAD_LIBS with CFLAGS=$PTHREAD_CFLAGS])
-        AC_TRY_LINK_FUNC(pthread_join, acx_pthread_ok=yes)
-        AC_MSG_RESULT($acx_pthread_ok)
-        if test x"$acx_pthread_ok" = xno; then
-                PTHREAD_LIBS=""
-                PTHREAD_CFLAGS=""
-        fi
-        LIBS="$save_LIBS"
-        CFLAGS="$save_CFLAGS"
-fi
-
-# We must check for the threads library under a number of different
-# names; the ordering is very important because some systems
-# (e.g. DEC) have both -lpthread and -lpthreads, where one of the
-# libraries is broken (non-POSIX).
-
-# Create a list of thread flags to try.  Items starting with a "-" are
-# C compiler flags, and other items are library names, except for "none"
-# which indicates that we try without any flags at all, and "pthread-config"
-# which is a program returning the flags for the Pth emulation library.
-
-acx_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config pthreadGC2"
-
-# The ordering *is* (sometimes) important.  Some notes on the
-# individual items follow:
-
-# pthreads: AIX (must check this before -lpthread)
-# none: in case threads are in libc; should be tried before -Kthread and
-#       other compiler flags to prevent continual compiler warnings
-# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
-# -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
-# lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)
-# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads)
-# -pthreads: Solaris/gcc
-# -mthreads: Mingw32/gcc, Lynx/gcc
-# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
-#      doesn't hurt to check since this sometimes defines pthreads too;
-#      also defines -D_REENTRANT)
-# pthread: Linux, etcetera
-# --thread-safe: KAI C++
-# pthread-config: use pthread-config program (for GNU Pth library)
-
-case "${host_cpu}-${host_os}" in
-        *solaris*)
-
-        # On Solaris (at least, for some versions), libc contains stubbed
-        # (non-functional) versions of the pthreads routines, so link-based
-        # tests will erroneously succeed.  (We need to link with -pthread or
-        # -lpthread.)  (The stubs are missing pthread_cleanup_push, or rather
-        # a function called by this macro, so we could check for that, but
-        # who knows whether they'll stub that too in a future libc.)  So,
-        # we'll just look for -pthreads and -lpthread first:
-
-        acx_pthread_flags="-pthread -pthreads pthread -mt $acx_pthread_flags"
-        ;;
-esac
-
-if test x"$acx_pthread_ok" = xno; then
-for flag in $acx_pthread_flags; do
-
-        tryPTHREAD_CFLAGS=""
-        tryPTHREAD_LIBS=""
-        case $flag in
-                none)
-                AC_MSG_CHECKING([whether pthreads work without any flags])
-                ;;
-
-                -*)
-                AC_MSG_CHECKING([whether pthreads work with $flag])
-                tryPTHREAD_CFLAGS="$flag"
-                ;;
-
-                pthread-config)
-                # skip this if we already have flags defined, for PostgreSQL
-                if test x"$PTHREAD_CFLAGS" != x -o x"$PTHREAD_LIBS" != x; then continue; fi
-                AC_CHECK_PROG(acx_pthread_config, pthread-config, yes, no)
-                if test x"$acx_pthread_config" = xno; then continue; fi
-                tryPTHREAD_CFLAGS="`pthread-config --cflags`"
-                tryPTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
-                ;;
-
-                *)
-                AC_MSG_CHECKING([for the pthreads library -l$flag])
-                tryPTHREAD_LIBS="-l$flag"
-                ;;
-        esac
-
-        save_LIBS="$LIBS"
-        save_CFLAGS="$CFLAGS"
-        LIBS="$tryPTHREAD_LIBS $PTHREAD_LIBS $LIBS"
-        CFLAGS="$CFLAGS $PTHREAD_CFLAGS $tryPTHREAD_CFLAGS"
-
-        # Check for various functions.  We must include pthread.h,
-        # since some functions may be macros.  (On the Sequent, we
-        # need a special flag -Kthread to make this header compile.)
-        # We check for pthread_join because it is in -lpthread on IRIX
-        # while pthread_create is in libc.  We check for pthread_attr_init
-        # due to DEC craziness with -lpthreads.  We check for
-        # pthread_cleanup_push because it is one of the few pthread
-        # functions on Solaris that doesn't have a non-functional libc stub.
-        # We try pthread_create on general principles.
-        AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>],
-                    [pthread_t th; pthread_join(th, 0);
-                     pthread_attr_init(0); pthread_cleanup_push(0, 0);
-                     pthread_create(0,0,0,0); pthread_cleanup_pop(0); ])],
-                    [acx_pthread_ok=yes], [acx_pthread_ok=no])
-
-        if test "x$acx_pthread_ok" = xyes; then
-            # Don't use options that are ignored by the compiler.
-            # We find them by checking stderror.
-            cat >conftest.$ac_ext <<_ACEOF
-int
-main (int argc, char **argv)
-{
-  (void) argc;
-  (void) argv;
-  return 0;
-}
-_ACEOF
-            rm -f conftest.$ac_objext conftest$ac_exeext
-            # Check both linking and compiling, because they might tolerate different options.
-            if test "`(eval $ac_link 2>&1 1>&5)`" = "" && test "`(eval $ac_compile 2>&1 1>&5)`" = ""; then
-                # The original macro breaks out of the loop at this point,
-                # but we continue trying flags because Linux needs -lpthread
-                # too to build libpq successfully.  The test above only
-                # tests for building binaries, not shared libraries.
-                PTHREAD_LIBS=" $tryPTHREAD_LIBS $PTHREAD_LIBS"
-                PTHREAD_CFLAGS="$PTHREAD_CFLAGS $tryPTHREAD_CFLAGS"
-            else   acx_pthread_ok=no
-            fi
-        fi
-
-        LIBS="$save_LIBS"
-        CFLAGS="$save_CFLAGS"
-
-        AC_MSG_RESULT($acx_pthread_ok)
-done
-fi
-
-# The original macro has a bunch of other tests here, which we have removed
-# because (a) Postgres doesn't need them, and (b) $acx_pthread_ok is not
-# meaningful at this point.
-
-AC_SUBST(PTHREAD_LIBS)
-AC_SUBST(PTHREAD_CFLAGS)
-
-AC_LANG_POP([C])
-])dnl ACX_PTHREAD

configure.in

@@ -1579,7 +1579,7 @@ fi
 # See the comment at the top of src/port/thread.c for more information.
 # WIN32 doesn't need the pthread tests;  it always uses threads
 if test "$enable_thread_safety" = yes -a "$PORTNAME" != "win32"; then
-ACX_PTHREAD	# set thread flags
+AX_PTHREAD	# set thread flags
 
 # Some platforms use these, so just define them.  They can't hurt if they
 # are not supported.  For example, on Solaris -D_POSIX_PTHREAD_SEMANTICS